Localized high-salt-concentration electrolytes containing longer-sidechain glyme-based solvents and fluorinated diluents, and uses thereof

ABSTRACT

Localized high-salt-concentration electrolytes each containing a salt, a glyme as a solvent, and a fluorinated diluent. In some embodiments, the glyme has a chemical formula R 1 —(O—CH 2 —CH 2 ) n —O—R 2 , wherein n=1 to 4 and at least one of R 1  and R 2  is a hydrocarbon sidechain having at least 2 carbon atoms and wherein the salt is soluble in the glyme. In some embodiments, the fluorinated diluent is selected from the group consisting of a fluorinated glyme and a fluorinated ether. In some embodiments, the salt includes an alkali-metal salt. In some embodiments, the salt includes an alkali-earth-metal salt. The salt may include a perfluorinated sulfonimide salt. Electrochemical devices that include localized high-salt-concentration electrolytes of the present disclosure are also disclosed.

RELATED APPLICATION DATA

This application claims the benefit of priority of U.S. ProvisionalPatent Application Ser. No. 62/832,676, filed Apr. 11, 2019, and titled“HIGH SALT CONCENTRATION ELECTROLYTES WITH DILUENTS FOR SECONDARYLITHIUM BATTERIES”, which is incorporated by reference herein in itsentirety.

FIELD OF THE INVENTION

The present invention generally relates to the field of electrolytes forelectrochemical devices. In particular, the present invention isdirected to localized high-salt-concentration electrolytes containinglonger-sidechain glyme-based solvents and fluorinated diluents, and usesthereof.

BACKGROUND

High-salt-concentration electrolytes are known to enhance cycle life inrechargeable, or secondary, batteries having lithium-metal anodes. Inparticular, electrolytes with greater than 2 molar (M) of LiFSI orLiTFSI salt dissolved in glyme-based solvents are known to enhancecharge-discharge cycle-life performance in batteries havinglithium-metal anodes. In conventional electrolytes having ˜1M lithiumsalt concentration, the solvent molecules undergo reduction at thesurface of the lithium-metal anode to form a solid-electrolyteinterphase (SEI) (passivation) layer. In a high-salt-concentrationlithium-based electrolyte, most of the solvent molecules will remainassociated with the solvated Li⁺ ions and are not available to form theSEI layer. In the absence of free solvent molecules, a more compact andstable SEI is formed on the lithium anode's surface by the fluorinatedanion of the lithium salt, which leads to higher lithiumplating/stripping coulombic efficiency and enhanced cycle lifeperformance of the battery.

High-salt-concentration electrolytes, however, have severaldisadvantages, such as low conductivity, high viscosity, and theconsequent poor wetting of electrodes and separator, resulting in lowercharge-discharge rates (C-rates) than those typically used inconventional secondary batteries. High-salt-concentration electrolytesalso incur higher production cost due to their high salt content, withthe salt typically being the most expensive constituent of theelectrolyte. Diluting high-salt-concentration electrolytes with excesssolvent creates more free-solvent molecules that react with and consumethe lithium-metal anode, thus reducing the coulombic efficiency andcycle life of the battery.

Furthermore, to offset the high viscosity caused by high saltconcentration, these electrolytes often make use of low-boiling-pointDME (1,2-Dimethoxyethane or monoglyme or Ethylene glycol dimethyl ether)as the solvent. Use of low boiling solvents such as DME typically leadsto significant gas generation in cells exposed to high ambienttemperature while in a charged state.

SUMMARY OF THE DISCLOSURE

In an implementation, the present disclosure is directed to anelectrolyte that includes a salt; a solvent comprising a glyme of theformula R₁—(O—CH₂—CH₂)_(n)—O—R₂, wherein n=1 to 4 and at least one of R₁and R₂ is a hydrocarbon sidechain having at least 2 carbon atoms,wherein the salt is soluble in the solvent; and a diluent selected fromthe group consisting of a fluorinated glyme and a fluorinated ether.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, the drawings show aspectsof one or more embodiments of the invention. However, it should beunderstood that the present invention is not limited to the precisearrangements and instrumentalities shown in the drawings, wherein:

FIG. 1A is a graph of cycle life versus lithium-salt concentration forseveral example localized high-salt-concentration (LHSC) electrolytes ofthe present disclosure, each composed of lithiumbis(fluorosulfonyl)imide salt (LiFSI), 1,2-11diethoxyethane (DEE), and1,2-(1,1,2,2-tetrafluoroethoxy)-ethane (TFE) and with differing DEE:TFEvolumetric percentage ratios;

FIG. 1B is a graph of cycle life versus DEE volume percentage fordiffering salt (LiFSI) concentrations of the LHSC electrolytes of FIG.1A;

FIG. 2 is a graph of cycle life versus DEE/LiFSI (solvent/salt) molarratio in the various LHSC electrolytes of FIGS. 1A and 1B;

FIG. 3A is a chart showing cycle life for a number of differingelectrolytes, including a 2M LiFSI+DEE+TFE LHSC electrolyte of thepresent disclosure having a 70:30 DEE:TFE volumetric percentage ratio;

FIG. 3B is a chart showing normalized gas generation for theelectrolytes of FIG. 3A; and

FIG. 4 is a high-level diagram illustrating an electrochemical devicemade in accordance with aspects of the present disclosure.

DETAILED DESCRIPTION

In some aspects, the present disclosure is directed to localizedhigh-salt-concentration (LHSC) electrolytes made using longer-sidechainglymes and fluorinated diluents. LHSC electrolytes made in accordancewith this disclosure may have a high concentration of lithium salt, suchas LiFSI or LiTFSI, for example, dissolved in a longer-sidechainglyme-based solvent, such as DEE (1,2-diethoxyethane or ethylene glyme),having one or more sidechains that extend the length of the molecularstructure of the base glyme, whether it be a monoglyme or polyglyme. Inthe context of a monoglyme, the base glyme is DME (1,2-dimethoxyethane).As used herein and in the appended claims, the term “longer-sidechainglyme-based solvent” denotes a glyme-based solvent having an additionalhydrocarbon molecular structure attached to at least one end of theglyme molecular structure. Examples of longer-sidechain glyme-basedsolvents are described in detail below. LHSC electrolytes made inaccordance with the present disclosure may also include a fluorinatedhydrocarbon, such as a fluorinated glyme or fluorinated ether, added asa diluent to overcome disadvantages usually associated withhigh-salt-concentration electrolytes.

The fluorinated diluent is typically miscible with the longer-sidechainglyme-based solvent used in the LHSC electrolyte, but it is designed orselected to have much lower lithium-salt solubility relative toglyme-based solvents by virtue of its low polarity. As a result, thesolvent molecules of the longer-sidechain glyme-based solvent and thelithium ions from the lithium-based salt will remain associated with oneanother even after the addition of diluent and thus retain theadvantages of a high-salt-concentration electrolyte. Moreover, theaddition of the fluorinated diluent decreases the overall viscosity andhelps improve the conductivity and wetting properties of the LHSCelectrolyte, without increasing the amount of free solvent molecules inthe electrolyte. In turn, this allows use of higher charge-dischargerates, for example, charge-discharge rates typically used inconventional secondary batteries such as lithium-ion batteries, withoutsacrificing the high coulombic efficiency and cycle life of the battery.In addition, as the diluent is fluorinated, it may also help form a morecompact and stable solid-electrolyte interphase (SEI) on, for example,the lithium-metal surface of the anode of a lithium-metal secondarybattery, in a manner analogous to the fluorinated anion of the lithiumsalt.

Furthermore, the fluorinated diluent also allows the use of the morestable longer-sidechain glyme-based solvents (such as DEE(1,2-diethoxyethane or ethylene glycol diethyl ether), DPE(1,2-dipropoxyethane or ethylene glycol dipropyl ether), DBE(1,2-dibutoxyethane or ethylene glycol dibutyl ether), diethylene glycoldiethyl ether, diethylene glycol dipropyl ether, triethylene glycoldibutyl ether, triethylene glycol diethyl ether, triethylene glycoldipropyl ether, triethylene glycol dibutyl ether, tetraethylene glycoldiethyl ether, tetraethylene glycol dipropyl ether, tetraethylene glycoldibutyl, etc.,) that, by themselves, are relatively more viscous thanDME in making high-salt-concentration electrolyte. Use of themore-stable longer-sidechain glyme-based solvents of the presentdisclosure, in turn, prevents or decreases gas generated in chargedelectrochemical cells exposed to high ambient temperatures. Thedecomposition products of the longer-sidechain glyme-based solventstypically would be relatively larger molecules having higher boilingpoints (relative to DME, for example) that may tend to dissolve moreinto the LHSC electrolyte instead of generating gas inside the cell. Inaddition, having one or more longer sidechains increases the molarvolume of the glyme-based solvent, which in turn decreases the amount ofsalt required per unit volume of the LHSC electrolyte (moleconcentration or molarity) to maintain association between the Li⁺ ionsand solvent molecules and, consequently, lowers the volumetric cost ofproducing the LHSC electrolyte.

In another aspect, the present disclosure is directed to uses oflithium-based LHSC electrolytes made in accordance with the presentdisclosure. For example, these LHSC electrolytes can be used in anysuitable lithium-based electrochemical device, such as a battery orsupercapacitor. Lithium-based LHSC electrolytes made in accordance withthe present disclosure can provide, for example, greatercharge-discharge cycle life and reduced gas production to theelectrochemical devices, while providing desirable wetting andSEI-formation characteristics and allowing for favorable C rates, amongother things.

Details of the foregoing and other aspects of the present disclosure aredescribed below.

Throughout the present disclosure, the term “about” when used with acorresponding numeric value refers to ±20% of the numeric value,typically ±10% of the numeric value, often ±5% of the numeric value, andmost often ±2% of the numeric value. In some embodiments, the term“about” can be taken as exactly indicating the actual numerical value.

Localized High-Salt-Concentration Electrolytes

Example Longer-Sidechain Glyme-Based Solvents

Structure 1, below, shows the general molecular structure of alonger-sidechain glyme R₁—(O—CH₂—CH₂)_(n)—O—R₂ that can be used in anLHSC electrolyte made in accordance with the present disclosure.Longer-sidechain glymes of this disclosure will have at least onesidechain structure (R₁ or R₂) that has 2 to 6 carbon atoms. Thesidechains can be linear, branched, cyclic, either partially orcompletely saturated. The sidechains can have the same or differentmolecular structure (i.e., R₁═R₂ or R₁≠R₂). Having a methyl (—CH₂)sidechain with one carbon atom on both sides (i.e., for each of R₁ andR₂) will yield DME, which, as noted above, is conventionally used assolvent in some high-concentration electrolytes. As also noted above,DME has some distinct drawbacks in some electrochemical cellapplications, such as secondary lithium-metal batteries.

For the sake of illustration, Structure 2, above, is the molecularstructure of DEE (1,2-diethoxyethane, or ethylene glyme, orCH3-CH2—O—CH2—CH2—O—CH2—CH3), wherein the sidechains R₁ and R2 are bothethyl (—CH2-CH3) groups. DEE is utilized below as an examplelonger-sidechain glyme-based solvent of the present disclosure. However,those skilled in the art will readily appreciate that DEE is merely anexample and is not intended to limit the selection of anotherlonger-sidechain glyme-based solvent, such as a solvent having theforegoing generalized molecular structure of Structure 1, above, for anLHSC electrolyte made in accordance with the present disclosure.

Example Fluorinated Diluents

In some embodiments, a high-salt-concentration electrolyte of thepresent disclosure may be made using a fluorinated hydrocarbon, such asa fluorinated glyme or a fluorinated ether. Structure 3, below,illustrates a fluorinated glyme in the form of1,241,1,2,2-tetrafluoroethoxy)-ethane (TFE).

TFE is used as an example fluorinated diluent herein, particularly incombination with the DEE longer-sidechain glyme-based solvent addressedin the section above. It is noted that the backbone structure of TFE issimilar to the backbone of DEE. Consequently, TFE and DEE are morelikely to be miscible with one another. The presence of 8 fluorine atomsin the TFE molecule makes it less polar such that the lithium salt willbe less soluble, for example, about 10 times or more less soluble, inTFE. Consequently, when selecting a diluent and solvent in accordancewith the present disclosure it can be desirable to select a diluent andsolvent having similar backbone structures.

Two additional examples of fluorinated diluents are illustrated inStructures 4 and 5, below.

The fluorinated diluent of Structure 4 is the fluorinated ether1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), and thefluorinated diluent of Structure 5 is the fluorinated etherbis(2,2,2-trifluoroethyl) ether (BTFE). The foregoing are but a fewexamples of fluorinated glymes and fluorinated ethers suitable for usein a high-salt-concentration electrolyte according to the presentdisclosure. In some embodiments, diluents of the present disclosureincludes suitable hydrocarbon molecules having at least one oxygen (—O—)linkage and at least one fluorine (—F) substitution.

Example Li-Based Salts

A number of lithium-based salts may be used to make ahigh-salt-concentration electrolyte of the present disclosure. Forexample, in some embodiments it is desirable to use lithiumbis(fluorosulfonyl)imide (LiFSI), the molecular structure of which isillustrated in Structure 6, below.

In some embodiments, it is desirable to use a lithium-based salt havingthe general formula (Li⁺)(CF₃—(CF₂)_(n)—SO₂—N⁻—SO₂—(CF₂)n—CF₃), whereinn≥0. The molecular structure of this general formula is illustrated inStructure 7, below. Structure 8, also below, illustrates the case inwhich n=0, which is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

It is noted that while lithium perfluorinated sulfonimide salts areexemplified herein, teachings of the present disclosure may beimplemented with other salts, such as alkali-metal-based salts andalkali-earth-metal-based salts, such as perfluorinated sulfonimide saltsbased on sodium or magnesium, to name a couple. In addition, saltscommonly used in lithium-ion batteries, such as LiPF₆, LiAsF₆, LiBF₄,LiBOB, Li-triflate, etc., can be used in high-salt-concentrationelectrolytes made in accordance with the present disclosure.

Broadly, an electrolyte made in accordance with the present disclosuremay have a salt concentration in a range of about 0.1M to about 10M,while in some embodiments the salt concentration may be desired in arange of about 1M to about 5M, and in other embodiments the saltconcentration may be desired in a range of about 2M to about 3M. In someembodiments, the solvent:diluent ratio of an electrolyte made inaccordance with the present disclosure may by in a range of about 10:90to 100:0. In some embodiments, the solvent:diluent ratio may be desiredto be in a range of about 40:60 to about 90:10, and in other embodimentsthe solvent:diluent ratio may be desired to be in a range of about 60:40to about 80:20.

Example High-Salt-Concentration Electrolytes and Test Data

The following example LHSC electrolytes utilize LiFSI as the salt, DEEas the longer-sidechain glyme-based solvent, and TFE as the fluorinateddiluent. A number of LHSC electrolyte compositions were made withvarious concentrations of the LiFSI salt (1M to 5M) and with differingvolumetric ratios of DEE:TFE (30% to 100%), and these compositions weretested for cycle life and gas formation.

Cycle life was tested using identical pouch-type secondary battery cellsbuilt using nickel-manganese-cobalt (NMC) cathodes, lithium-metalanodes, and microporous polyolefin-based separators. During testing, thecells, containing corresponding ones of the LHSC electrolytecompositions, were cycled between 3V to 4.3V at a C/3-C/2charge-discharge rate. The Table below shows the charge-discharge cyclelife attained (at 80% capacity retention) in lithium cells made withvarious LiFSI+DEE+TFE LHSC electrolyte compositions of this disclosure.In the below Table, the cycle lives for DEE:TFE ratios at which theLiFSI salt of the corresponding concentration were not completelysoluble are denoted by a “-”. In general, with higher diluent (here,TFE) amounts, less LiFSI salt could be dissolved in the LHSCelectrolyte, since TFE is a fluorinated glyme having low polarity andsalt solubility.

TABLE Cycle Life LiFSI DEE:TFE volume ratio conc. 30:70 50:50 70:30100:0 1M 87 90 72 20 2M 43 106 140 80 3M — 47 124 115 4M — — 61 85 5M —— — 50

Turning now to the accompanying drawings, FIG. 1A shows the variation incycle life with respect to the lithium salt concentration of the variousLiFSI+DEE+TFE LHSC electrolyte compositions noted above, and FIG. 1Bshows the variation in cycle life with respect to DEE volume percentagefor those electrolyte compositions. As seen in FIGS. 1A and 1B and ingeneral, cycle life of the cells tends to be high near 2M or 3M lithiumsalt concentration and near 70:30 DEE:TFE volume ratio.

FIG. 2 shows the variation in cycle life with respect to thesolvent/salt (DEE/LiFSI) molar ratio in the LHSC electrolyte, regardlessof the diluent (TFE) amount. It has been known that a 2:1 solvent/saltmolar ratio in a conventional high-salt-concentration lithium-basedelectrolyte is optimal for cycle-life performance of a cell, since eachlithium ion associates with an average of two DME molecules in theelectrolyte. In this regard, FIG. 2 also indicates enhanced cycle lifefor cells with LHSC electrolytes of this disclosure having solvent:salt(DEE/LiFSI) molar ratio about 2:1. This corroborates the fact that thesolvent (DEE) molecules and solvated lithium ions remain associated evenafter the addition of the TFE diluent, thus retaining the advantages ofa high-salt-concentration electrolyte, while improving thecharging-discharging rate performance of the cell. In some embodiments,the solvent:salt molar ratio is in a range of about 1:1 to about 4:1. Insome embodiments, the solvent:salt ratio is in a range of about 1.5:1 toabout 3:1. A solvent:salt molar ratio of 2:1 for DEE/LiF SI roughlycorresponds to about 3.6 moles of LiFSI salt for every liter of DEEsolvent in the electrolyte. When the solvent: salt molar ratio is 2:1,those skilled in the art will understand that the (solvent+diluent):saltmolar ratio will be greater than 2:1. This is so for the simple reasonthat 2:1 is the molar ratio for the solvent alone, whereas the additionof diluent in the combination of the solvent+diluent increases thenumber of moles on the left-hand side of the molar ratio. For example,for the 70:30 DEE/TFE (solvent/diluent) volume ratio in the precedingparagraph with LiFSI as the salt, when the solvent:salt molar ratio is2:1, the (solvent+diluent):salt molar ratio is 2.7:1. As other examplesutilizing LiFSI, DEE, TFE, and a solvent:salt molar ratio of 2:1: at a50:50 solvent:diluent volume ratio, the (solvent+diluent):salt molarratio is 3.6:1, at a 60:40 solvent:diluent volume ratio, the(solvent+diluent):salt molar ratio is 3.1:1, at an 80:20 solvent:diluentvolume ratio, the (solvent+diluent):salt molar ratio is 2.4:1, and at a90:10 solvent: diluent volume ratio, the (solvent+diluent):salt molarratio is 2.2:1.

FIG. 3A compares the cycle life attained with various electrolytes incells that were cycled between 3 to 4.3V at C/3-C/2 charge-dischargerate. The LHSC electrolyte of this disclosure having a longer-sidechainglyme-based solvent and a fluorinated glyme diluent (the LHSCelectrolyte labeled “2M DEE:TFE (70:30)” in FIG. 3A) shows highercycle-life performance than “Conventional” carbonate-based electrolytesand high-salt-concentration electrolytes (labeled “5M DME”, “5M DEE”,and “2M DEE” in FIG. 3A) containing no diluent. In this context,“Conventional” carbonate-based electrolytes include electrolytes usingLiFSI, a cyclic carbonate solvent (e.g., EC (Ethylene Carbonate) or FEC(Fluorinated Ethylene Carbonate)), and optionally a linear carbonatediluent (e.g., EMC (Ethyl Methyl Carbonate). In an example, a“Conventional” electrolyte in this context may be a 1M to 3M LiFSIsolution in EC, and in another example, a “Conventional” electrolyte inthis context may be a 1M to 3M LiFSI solution in FEC:EMC in a 2:8volumetric ratio.

In addition, the use of more-stable longer-sidechain glyme-basedsolvent, such as DEE, would decrease the amount of gas generated incharged cells exposed to high ambient temperatures. FIG. 3B shows therelative amounts of gas generated by various electrolytes in fullycharged (state-of-charge (SOC) 100) pouch cells (described above)exposed for a week to 45° C. ambient temperature.Carbonate-solvent-based electrolytes conventionally used in lithium-ionbatteries produced the most amount of gas in the cell. Gas-suppressingadditives in the carbonate electrolyte did not yield any significantreduction in gas volume. The high-salt-concentration electrolyte(labeled “5M DME” in FIG. 3B) made with monoglyme solvent also showedgas generation similar to that of the carbonate-based electrolytes. Theuse of longer-sidechain glymes-based solvent, such as DEE, inhigh-salt-concentration electrolyte result in significant reduction ingas volume (labeled “5M DEE” in FIG. 3B). Furthermore, the LHSCelectrolyte composition of this disclosure in this example (labeled “2MLiFSI in DEE:TFE (70:30)” in FIG. 3B) having enhanced cycle-lifeperformance, also shows a significantly lower gas generation.

The lower gas generation along with enhanced cycle-life performance athigher charge-discharge rates makes the LHSC electrolytes of the presentdisclosure, which contain a longer-sidechain glyme-based solvent and afluorinated-glyme or fluorinated-ether diluent, target electrolytes forlithium-metal electrochemical devices, such as secondary batteries andsupercapacitors.

Example Uses of LHSC Electrolytes of the Present Disclosure

As mentioned above, an LHSC electrolyte of the present disclosure may beused as an electrolyte for an electrochemical device, among otherthings. FIG. 4 illustrates an electrochemical device 400 made inaccordance with aspects of the present disclosure. Those skilled in theart will readily appreciate that the electrochemical device 400 can be,for example, a battery or a supercapacitor. In addition, those skilledin the art will readily understand that FIG. 4 illustrates only somebasic functional components of the electrochemical device 400 and that areal-world instantiation of the electrochemical device, such as asecondary battery or a supercapacitor, will typically be embodied usingeither a wound construction or a stacked construction. Further, thoseskilled in the art will understand that the electrochemical device 400will include other components, such as electrical terminals, seal(s),thermal shutdown layer(s), and/or vent(s), among other things, that, forease of illustration, are not shown in FIG. 4.

In this example, the electrochemical device 400 includes spaced-apartpositive and negative electrodes 404, 408, respectively, and a pair ofcorresponding respective current collectors 404A, 408A. A porousdielectric separator 412 is located between the positive and negativeelectrodes 404, 408 to electrically separate the positive and negativeelectrodes but to allow ions of an LHSC electrolyte 416 made inaccordance with the present disclosure to flow therethrough. The porousdielectric separator 412 and/or one, the other, or both of the positiveand negative electrodes 404, 408, if porous, is/are impregnated with theLHSC electrolyte 416. In FIG. 4, both the positive and negativeelectrodes 404, 408 are illustrated as being porous by way of the LHSCelectrolyte 416 being illustrated as extending into them. In someembodiments, such as certain embodiments of lithium-metal secondarybatteries having solid-type lithium-metal negative electrodes, one, theother, or both of the positive and negative electrodes 404, 408 need notbe porous. As described above, benefits of using an LHSC electrolyte ofthe present disclosure for LHSC electrolyte 416 can include the factsthat less salt is needed than in DME-based electrolytes because of thelarger molecules of the longer-sidechain glyme-based solvent and thefluorinated diluent, less gas is produced at higher temperatures,cycle-life performance is enhanced, higher coulombic efficiency arepossible, and higher charging-discharging rates are possible. Examplesof LHSC electrolytes suitable for use as the LHSC electrolyte 416 aredescribed above. In some deployments, LHSC electrolytes of the presentdisclosure are particularly suited for use in cyclable lithium-metalbased electrochemical devices, such as secondary lithium-metalbatteries. As disclosed herein, various compositions of LHSCelectrolytes of the present disclosure can yield cycle-life performancesuperior to other types of electrolytes. The electrochemical device 400includes a container 420 that contains the current collectors 404A,408A, the positive and negative electrodes 404, 408, the porousdielectric separator 412, and the LHSC electrolyte 416.

As those skilled in the art will understand, depending upon the type anddesign of the electrochemical device, each of the positive and negativeelectrodes 404, 408 comprises a suitable material compatible with thealkali-metal ions and other constituents in the LHSC electrolyte 416.Each of the current collectors 404A, 408A may be made of any suitableelectrically conducting material, such as copper or aluminum, or anycombination thereof. The porous dielectric separator 412 may be made ofany suitable porous dielectric material, such as a porous polymer, amongothers. Various battery and supercapacitor constructions that can beused for constructing the electrochemical device 400 of FIG. 4, areknown in the art. If any of such known constructions is used, a noveltyof electrochemical device 400 lies in the composition of the LHSCelectrolyte 416.

In some aspects, the present disclosure is direct to an electrolytecomprising: a salt; a solvent comprising a glyme of the formulaR₁—(O—CH₂—CH₂)_(n)—O—R₂, wherein n=1 to 4 and at least one of R₁ and R₂is a hydrocarbon sidechain having at least 2 carbon atoms, wherein thesalt is soluble in the solvent; and a diluent selected from the groupconsisting of a fluorinated glyme and a fluorinated ether.

In one or more embodiments of the electrolyte, the salt comprises analkali-metal salt.

In one or more embodiments of the electrolyte, the salt comprises aperfluorinated sulfonimide salt.

In one or more embodiments of the electrolyte, the perfluorinatedsulfonimide salt comprises a lithium-based perfluorinated sulfonimidesalt.

In one or more embodiments of the electrolyte, the lithium-basedperfluorinated sulfonimide salt comprises lithiumbis(fluorosulfonyl)imide.

In one or more embodiments of the electrolyte, the salt comprises alithium-based salt.

In one or more embodiments of the electrolyte, the salt has aconcentration in the electrolyte in a range of about 0.1M to about 10M.

In one or more embodiments of the electrolyte, the salt has aconcentration in the electrolyte in a range of about 1M to about 5M.

In one or more embodiments of the electrolyte, the salt has aconcentration in the electrolyte in a range of about 2M to about 3M.

In one or more embodiments of the electrolyte, the electrolyte has avolumetric solvent:diluent percentage ratio of about 10:90 to about100:0.

In one or more embodiments of the electrolyte, the electrolyte has avolumetric solvent:diluent percentage ratio of about 40:60 to about90:10.

In one or more embodiments of the electrolyte, the electrolyte has avolumetric solvent:diluent percentage ratio of about 60:40 to about80:20.

In one or more embodiments of the electrolyte, the electrolyte has asolvent:salt molar ratio in a range of about 1:1 to about 4:1.

In one or more embodiments of the electrolyte, the electrolyte has asolvent:salt molar ratio in a range of about 1.5:1 to about 3:1.

In one or more embodiments of the electrolyte, the electrolyte has asolvent:salt molar ratio in a range of about 2:1.

In one or more embodiments of the electrolyte, R₁═R₂.

In one or more embodiments of the electrolyte, the hydrocarbon sidechainhas 2 to 6 carbon atoms.

In one or more embodiments of the electrolyte, n=1 and each of R₁ and R2is an ethyl group, as in 1,2-diethoxyethane (DEE).

In one or more embodiments of the electrolyte, the diluent comprises afluorinated ether.

In one or more embodiments of the electrolyte, the diluent comprises afluorinated glyme.

In one or more embodiments of the electrolyte, the fluorinated glyme is1,2-(1,1,2,2-tetrafluoroethoxy)-ethane (TFE).

In one or more embodiments of the electrolyte, the salt compriseslithium bis(fluorosulfonyl)imide.

In one or more embodiments of the electrolyte, the concentration of thesalt is at least 2M.

In one or more embodiments of the electrolyte, the solvent and thediluent are present in a solvent:diluent volumetric percentage ratio inwhich the solvent is at least 40% and the diluent is no more than 60%.

In one or more embodiments of the electrolyte, the solvent and thediluent are present in a solvent:diluent volumetric percentage ratio inwhich the solvent is at least 60% and the diluent is no more than 40%.

In one or more embodiments of the electrolyte, the concentration of thesalt is at least 3M.

In one or more embodiments of the electrolyte, the solvent and thediluent are present in a solvent:diluent volumetric percentage ratio inwhich the solvent is at least 40% and the diluent is no more than 60%.

In one or more embodiments of the electrolyte, the solvent and thediluent are present in a solvent:diluent volumetric percentage ratio inwhich the solvent is at least 60% and the diluent is no more than 40%.

In one or more embodiments of the electrolyte, the salt compriseslithium bis(fluoro-sulfonyl)imide.

In one or more embodiments of the electrolyte, the salt is selected fromthe group consisting of lithium bis(fluorosulfonyl)imide and a salt of amolecular structure:

wherein n is equal to or greater than 0.

In some aspects, the present disclosure is directed to anelectrochemical device, comprising: a positive electrode; a negativeelectrode spaced from the positive electrode; a porous dielectricseparator located between the positive and negative electrodes; and theelectrolyte according to any one of the foregoing electrolyteembodiments contained within at least the porous dielectric separator.

In one or more embodiments of the electrochemical device, the negativeelectrode comprises a lithium metal.

In one or more embodiments of the electrochemical device, theelectrochemical device is a secondary battery and the negative electrodeis a lithium metal electrode.

The foregoing has been a detailed description of illustrativeembodiments of the invention. It is noted that in the presentspecification and claims appended hereto, conjunctive language such asis used in the phrases “at least one of X, Y and Z” and “one or more ofX, Y, and Z,” unless specifically stated or indicated otherwise, shallbe taken to mean that each item in the conjunctive list can be presentin any number exclusive of every other item in the list or in any numberin combination with any or all other item(s) in the conjunctive list,each of which may also be present in any number. Applying this generalrule, the conjunctive phrases in the foregoing examples in which theconjunctive list consists of X, Y, and Z shall each encompass: one ormore of X; one or more of Y; one or more of Z; one or more of X and oneor more of Y; one or more of Y and one or more of Z; one or more of Xand one or more of Z; and one or more of X, one or more of Y and one ormore of Z.

Various modifications and additions can be made without departing fromthe spirit and scope of this invention. Features of each of the variousembodiments described above may be combined with features of otherdescribed embodiments as appropriate in order to provide a multiplicityof feature combinations in associated new embodiments. Furthermore,while the foregoing describes a number of separate embodiments, what hasbeen described herein is merely illustrative of the Applications of theprinciples of the present invention. Additionally, although particularmethods herein may be illustrated and/or described as being performed ina specific order, the ordering is highly variable within ordinary skillto achieve aspects of the present disclosure. Accordingly, thisdescription is meant to be taken only by way of example, and not tootherwise limit the scope of this invention.

Exemplary embodiments have been disclosed above and illustrated in theaccompanying drawings. It will be understood by those skilled in the artthat various changes, omissions and additions may be made to that whichis specifically disclosed herein without departing from the spirit andscope of the present invention.

What is claimed is:
 1. An electrolyte, consisting of: a salt; a solventthat is a glyme of the formula R₁—(O—CH₂—CH₂)_(n)—O—R₂, wherein n=1 to 4and at least one of R₁ and R₂ is a hydrocarbon sidechain having at least2 carbon atoms, wherein the salt is soluble in the solvent; and adiluent selected from the group consisting of a fluorinated glyme and afluorinated ether; wherein: the salt has a concentration in theelectrolyte of about 0.2 M to less than 5 M; the electrolyte has a(solvent+diluent):salt molar ratio in a range of greater than 2:1 toabout 8:1; and the electrolyte has a volumetric solvent:diluentpercentage ratio of about 50:50 to about 90:10.
 2. The electrolyte ofclaim 1, wherein the salt comprises a lithium-based salt.
 3. Theelectrolyte of claim 1, wherein the concentration of the salt is in arange of about 1M to less than 5M.
 4. The electrolyte of claim 1,wherein the concentration of the salt is in a range of about 2M to about3M.
 5. The electrolyte of claim 1, having a solvent:salt molar ratio ina range of about 2:1 to about 4:1.
 6. The electrolyte of claim 1, havinga solvent:salt molar ratio in a range of about 2:1 to about 3:1.
 7. Theelectrolyte of claim 1, having a solvent:salt molar ratio is about 2:1.8. The electrolyte of claim 1, wherein R₁=R₂.
 9. The electrolyte ofclaim 1, wherein the hydrocarbon sidechain has 2 to 6 carbon atoms. 10.The electrolyte of claim 1, wherein the salt is selected from the groupconsisting of lithium bis(fluorosulfonyl)imide and a salt of a molecularstructure:

wherein n is equal to or greater than
 0. 11. The electrolyte of claim 1,wherein the concentration of the salt is in a range of about 0.2M toabout 4M.
 12. The electrolyte of claim 1, wherein the volumetricsolvent:diluent percentage ratio of the electrolyte is about 60:40 toabout 80:20.
 13. The electrolyte of claim 12, wherein the concentrationof the salt is in a range of about 0.2M to about 4M.
 14. The electrolyteof claim 1, wherein the concentration of the salt is at least 2M. 15.The electrolyte of claim 14, wherein, in the solvent:diluent volumetricpercentage ratio, the solvent is at least 50% and the diluent is no morethan 50%.
 16. The electrolyte of claim 14, wherein, in thesolvent:diluent volumetric percentage ratio, the solvent is at least 60%and the diluent is no more than 40%.
 17. The electrolyte of claim 1,wherein n=1 and each of R₁ and R₂ is an ethyl group, as in1,2-diethoxyethane (DEE).
 18. The electrolyte of claim 17, wherein thediluent comprises a fluorinated ether.
 19. The electrolyte of claim 17,wherein the diluent comprises a fluorinated glyme.
 20. The electrolyteof claim 17, wherein the fluorinated glyme is1,2-(1,1,2,2-tetrafluoroethoxy)-ethane (TFE).
 21. The electrolyte ofclaim 20, wherein the salt comprises lithium bis(fluorosulfonyl)imide.22. The electrolyte of claim 1, wherein the concentration of the salt isless than about 3M.
 23. The electrolyte of claim 22, wherein, in thesolvent:diluent volumetric percentage ratio, the solvent is at least 50%and the diluent is no more than 50%.
 24. The electrolyte of claim 22,wherein, in the solvent:diluent volumetric percentage ratio, the solventis at least 60% and the diluent is no more than 40%.
 25. The electrolyteof claim 24, wherein the salt comprises lithiumbis(fluoro-sulfonyl)imide.
 26. The electrolyte of claim 1, wherein thesalt comprises an alkali-metal salt.
 27. The electrolyte of claim 26,wherein the salt comprises a perfluorinated sulfonimide salt.
 28. Theelectrolyte of claim 27, wherein the perfluorinated sulfonimide saltcomprises a lithium-based perfluorinated sulfonimide salt.
 29. Theelectrolyte of claim 28, wherein the lithium-based perfluorinatedsulfonimide salt comprises lithium bis(fluorosulfonyl)imide.